Double acting refrigeration compressor

ABSTRACT

The refrigeration compressor is a double-acting refrigeration compressor, comprising a piston which is freely guided on two cylinder sections that are opposite each other and that cannot be moved relative to each other, and which has a flow channel that extends internally through the piston, wherein each cylinder section and the piston have at least one check valve along the flow channel, wherein the check valves are arranged in such a way that the flow directions thereof are oriented in the same direction.

The present invention relates to a double-acting refrigerant compressor.

In the field of the recycling of refrigerants from cooling systems,particularly from air conditioning systems, a requirement exists for theuse of external compressors which, under the conditions prevailing atthe site of use of the air conditioning system, are capable to pump offthe refrigerant from the cooling system and to transfer it into acorresponding transport container.

For this purpose, the required compressors have to generate a gaspressure in the bottle that is above the steam pressure of therefrigerant at the respective ambient temperatures. In the extreme case,this gas pressure can be distinctly above 30 bar so that the furtherassumptions will have to be based on a working pressure of maximally 40bar.

In known recycling devices for transfer of the refrigerant from arefrigeration system into a recycling container, the recycling device isprovided with a compressor and with a bypass line shunting thecompressor. The compressor line and the bypass line are each providedwith valves, wherein, first, the pressurized refrigerant will flowthrough the bypass line into the recycling container. After completionof the pressure compensation between the recycling container and therefrigeration system, the residual refrigerant will be transferred intothe recycling container via the compressor of the recycling device whilethe bypass line is closed.

It is an object of the invention to provide a refrigerant compressorwhich is of a simple and inexpensive design and which achieves the highcompression performance required for recovery of the refrigerant.

The refrigerant compressor according to the invention is defined by thefeatures indicated in claim 1. Thus, the refrigerant compressor is adouble-acting refrigerant compressor comprising a piston which is freelyguided on two mutually opposite cylinder portions. The cylinder portionsare not movable relative to each other. The piston comprises a flowchannel extending through the interior of the piston. Each cylinderportion and the piston are provided, along the flow channel, with atleast one back-check valve, with the flow-through direction of saidback-check valves being unidirectional.

Said cylinder portions can be provided as components of a one-piecedcylinder or as separate components. It is decisive that the cylinderportions are not movable relative to each other and that the piston isguided in the cylinder portions freely, i.e. without a connection toother component parts such as e.g. piston rods, and in a sealed manner.An internal flow channel extends through the entire piston from onepiston end to the opposite piston end. In the region of the flowchannel, the piston comprises at least one back-check valve. Also eachcylinder portion comprises at least one back-check valve. Preferably,the flow channel is formed along a linear longitudinal axis along whichalso said back-check valves are arranged. The flow-through directions ofthe back-check valves are unidirectional, which is to say that, with arefrigerant flowing through the piston in a first flow direction, theback-check valves are open and, with a refrigerant flowing through thepiston in a second flow direction opposite to the first flow direction,the back-check valves are closed.

In this manner, it is rendered possible that the refrigerant of arefrigeration system, being under a high pressure of e.g. 40 bar, can betransferred into a recycling container having a low pressure, withoutentailing the necessity of a separate bypass line. Upon completion ofthe pressure compensation between the refrigeration system and therecycling container, the piston, during a stroke movement, will suck inthe refrigerant from the refrigeration system in the direction of therecycling container via the back-check valve of that cylinder portionwhich is facing toward the refrigeration system. During the subsequentopposite stroke movement of the piston from the recycling container inthe direction of the refrigeration system, the back-check valve of thepiston will open, and the refrigerant previously sucked from therefrigeration system will now flow through the piston via the interiorflow channel to the opposites side of the piston facing toward therecycling container. Upon renewed reversal of the stroke movement, theback-check valve of the piston will close, and the piston will press therefrigerant through the back-check valve of the cylinder portion facingthe recycling container, and in the direction of the recyclingcontainer.

The advantage of the refrigerant compressor of the invention resides inobviating the necessity for a separate bypass line for removal ofrefrigerant from a refrigeration system and into a recycling containeruntil pressure compensation has been reached. The inner flow channel canbe realized in a simple manner, e.g. as a bore. By the piston which isfreely guided in the respective cylinder portions, no need exists forthe use of seals for the connection of outer mechanics to the pistonthrough the cylinder. The only required seals are to be provided in theregion of the back-check valves and of the contact areas between thepiston and the cylinder portions.

In case of rotationally symmetrical cylinder portions and pistons withbackcheck valves and with a flow channel on the central longitudinalaxis, the refrigerant compressor of the invention can be produced in aparticularly simple manner by turning and drilling.

Between the cylinder portions, there is preferably provided such adistance that a region of the piston is freely accessible from theoutside for allowing access to the piston and its drive unit withouthaving to fit seals through the cylinder portions.

Advantageously, the piston comprises, between its two end-sidecompression surfaces, an auxiliary compression surface which togetherwith one of the two cylinder portions forms an auxiliary volume which,during a stroke movement of the piston effected by a driving force, willgenerate a restoring force acting against the driving force.

It is of particular advantage if at least one of the two cylinderportions is guided as an inverse piston in said piston so that thepiston encloses the respective cylinder portions on the outside and isfreely accessible from there, e.g. for gaining access to the drive unit.Particularly, both cylinder portions can be guided as inverse pistons insaid piston, wherein the two cylinder portions are immobile relative toeach other and only the piston will perform a movement.

The piston can be driven in a contactless manner by two solenoidsoperating in opposite senses, e.g. in the form of a flat-armature driveor a plunger-armature drive. In case of the flat-armature drive, thearmature plate advantageously extends through the interspace between thetwo cylinder portions into the magnetic field generated by the solenoid.Theoretically, in this regard, one of the two solenoids could bereplaced by a spring drive. In case of a plunger-armature drive, thepiston can be fully inserted as a plunger armature into the interior ofa one-pieced cylinder.

Alternatively, an eccentric guide system of a crankshaft drive could beconnected to the piston through the interspace between the two cylinderportions, or a rotary drive could—via a nose element—engage an 8-shapedsliding path on the surface of the piston.

Embodiments of the invention will be described in greater detailhereunder with reference to the Figures. In the Figures, the followingis shown:

FIG. 1 shows the first embodiment in a first operating state,

FIG. 2 shows the first embodiment in a second operating state,

FIG. 3 shows a second embodiment in a first operating state,

FIG. 4 shows the second embodiment in a second operating state,

FIG. 5 shows a third embodiment in a first operating state,

FIG. 6 shows the third embodiment in a second operating state,

FIG. 7 shows a fourth embodiment in a first operating state,

FIG. 8 shows the fourth embodiment in a second operating state,

FIG. 9 shows a fifth embodiment,

FIG. 10 shows a sixth embodiment,

FIG. 11 shows a seventh embodiment,

FIG. 12 shows an eighth embodiment, and

FIG. 13 shows a ninth embodiment.

In the refrigerant compressor according to the first embodiment shown inFIGS. 1 and 2, the compressor system comprises the stepped cylinder 1 inwhich the piston 7 with the central overflow channel 8 is guided inaxial direction. The cylinder is terminated by the inlet valve plate 2and the outlet valve plate 3 in which the inlet valve 10 andrespectively the outlet valve 12 are inserted. Overflow channel 8 isterminated by a further valve 11 on the side where the outlet islocated.

In this arrangement, the larger-diametered left portion of the steppedcylinder 1 forms the first cylinder portion 41, and thesmaller-diametered right-hand portion of the stepped cylinder 1 formsthe second cylinder portion 42. Thus, the two cylinder portions 41 and42 are integrally connected and form the cylinder 1.

The basic function of the double-acting inline free-piston compressor isto be described as follows:

By means of a drive, not yet to be described here, the piston will bebrought into a linear oscillatory movement. This can be performed as aresonance oscillation or as a forced oscillation.

Under the functional aspect, the compressor has three characteristicvolumes which will influence the work of the system and will determinethe force development:

-   -   the low-pressure working volume 4    -   the high-pressure working volume 6    -   the auxiliary volume 5 which assists in controlling the piston        (optimally by use of a bypass to the left before valve 10, or to        the right from valve 12)

When piston 7 moves to the left, the medium in the low-pressure workingvolume 4 will be displaced. Since, due to the pressure increase, valve10 will close, the medium will be forced via overflow channel 8 andoverflow valve 11 into the enlarging high-pressure working volume 6.Achieved thereby is a precompression of the medium, said precompressionbeing determined approximately by the ratio between the cylinder crosssections of the low-pressure working volume 4 and the cross section ofthe high-pressure working volume 6.

As soon as the piston has reached its left-hand turning point, themovement is reversed. The medium will now be displaced from thehigh-pressure working volume 6 and, via outlet valve 12, will enter theoutlet. At the same time, the low-pressure working volume 4 will becomelarger. The pressure drop in the low-pressure working volume 4 and theincrease of the pressure in the high-pressure working volume 6 willcause the overflow valve 11 to be closed. At the same time, the mediumwill be sucked in from the inlet via inlet valve 10.

As soon as the piston has reached its right-hand turning point, themovement is reversed again and the process is repeated.

In the operational mode for the recycling of refrigerant, the aboveconstruction has the advantage that a passive pressure compensation willtake place between the inlet and the outlet. In this use, theconventionally required bypass of the state of the art can be omitted.By the construction of the double-acting inline free-piston compressor,the medium can directly flow over through the inlet valve 10, theoverflow valve 11 and the outlet valve 12. This can occur as a liquidphase and as a gaseous phase.

After pressure compensation, the steam pressure of the refrigerant,which in the present case can be assumed to be 40 bar, will exist in thelow-pressure working volume 4 and in the high-pressure working volume 6.Now, the pressure in the auxiliary volume 5 will take a considerableinfluence on the force/path behavior of the system.

-   Variant 1: The volume is vented into the ambience. The pressure will    thus always be the normal pressure of 1 bar.-   Variant 2: The volume is gas-tight and is realized with a constant    prepressure p₀ as a gas-pressured spring.-   Variant 3: The volume is connected to the inlet line so that the    prepressure is equal to the working pressure in the refrigeration    system.-   Variant 4: The volume is connected to the outlet line so that the    prepressure in the auxiliary volume is equal to the working pressure    in the recycling container.

A modification of the first embodiment is obtained by opening thecylinder in the middle, so that, as a second embodiment, there isrealized a design as depicted in FIGS. 3 and 4 wherein the firstcylinder portion 41 is spaced apart from the second cylinder portion 42.Dividing the cylinder into two mutually spaced cylinder portions 41,42allows for a direct mechanical access to the piston and, thus, also fora drive by use of form-locking engagement.

A further modification results in the third embodiment according toFIGS. 5 and 6 with an inverse compression chamber. The compressor withinverse compression chamber consists of the piston 25 with the overflowchannel 8, of the intermediate valve 11 and of the inverse compressionchamber 6. The piston 25 is guided in the cylinder 24 which isterminated by the inlet valve plate 2. In the inlet valve plate 2, theinlet valve 10 is mounted. Inlet valve plate 2, cylinder 24 and piston25 form the low-pressure working volume 4.

Inserted within the inverse compression chamber 6 is the fixed inversepiston 23 with the outlet channel and the outlet valve 12. The cylinder24 and the inverse piston 23 are tightly connected to each other via asupport rack, not illustrated here, and form the stationary system ofthe compressor.

An advantage of this arrangement is the direct mechanical access to thepiston while maintaining the inline flow of the medium, so that, on theone hand, the driving of the piston can also be performed with forcedguidance, e.g. by means of a crank drive, and, on the other hand, themedium can flow directly from the inlet through all valves to theoutlet.

In the fourth embodiment according to FIGS. 7 and 8, both cylinderportions 41 and 42 are guided as inverse pistons in piston 25.

The fifth embodiment according to FIG. 9 comprises a flat-armature drivefor driving the piston. The piston, which itself can be made of amaterial not relevant for the drive, is mechanically connected to thearmature plate 52 made of magnetically soft iron. On both sides, thereis arranged a respective pot magnet consisting of the iron core 50 or 54and of the electric coil 51 or 53. By energizing the coils alternatelyfrom both sides, a respective magnetic field is generated between thepot magnet and the armature plate which causes the armature to performthe corresponding movement. For control of the energization, positionsensors are required for the piston. In the most simple case, such asensor can be provided as a slider switch which is operative to switchthe energy supply to the other coil when a predetermined end positionhas been reached.

Other concepts can provide the use of additional electronic elementswhich will realize the switching not only in dependence on the positionbut will also include e.g. the speed and the load into the controlprocess. An advantage of this drive resides in that the flat armaturehas a force/path development which is adaptable to that of thecompressor in a favorable manner. Along with a decrease of the air gapbetween the armature and the magnet, the force will rise in anoverproportionate manner, thus allowing particularly the application ofthe high forces in the piston end positions.

In the sixth embodiment according to FIG. 10, a magnetic spring drive isused for the piston. The operating principle herein consists in aspring-mass oscillator wherein the piston as the mass is excited toperform an oscillating movement. The work to be delivered by the machinehas a damping effect and has to be performed as synchronous excitationby the magnet. The principle is very effective for smaller workingcapacities. To allow for an oscillation to really occur, the kinetic orpotential energy stored in the spring-mass system has to be larger thanthe work to be delivered.

In the seventh embodiment according to FIG. 11, a plunger-type armatureis used as a drive for the piston. The coils will generate, in a manneralternating between the two sides, a magnetic flux in the left and inthe right region of the plunger armature. The armature will then eachtime be pulled into the corresponding end position. Also here, it isimperative to achieve an optimized controlling of the coil so as toavoid an unbraked impacting of the armature. Control of the coils isperformed in the same manner as in the flat-armature drive.

In the embodiment according to FIG. 12, the piston 7 is driven by aconventional crank drive via an eccentric guide arrangement 61comprising a shaft 60. Operation of the symmetrically arranged shaft 60of the rotary drive can be converted into forced oscillation by methodswhich are also known per se. This approach can be used both for thenormal constructional design and for the design with inverse compressionchamber. Of advantage herein is the use of normal rotary drives and theforced control of the path.

Alternatively, if a conventional drive is provided, a rotary drive 71 asin FIG. 13, with its rotary axis corresponding to the centrallongitudinal axis of piston 7, can also serve for engaging, by aninterior nose 72, an 8-shaped sliding track 73 arranged on the outercircumferential surface of the piston 7 so that, by rotation of rotarydrive 71, piston 7 will be caused to perform an oscillating strokemovement.

1. A double-acting refrigerant compressor comprising a piston freelyguided on two cylinder portions arranged opposite to each other andbeing immobile relative to each other, said piston comprising a flowchannel extending internally through the piston, each cylinder portionand the piston comprising, along the flow channel, respectively at leastone back-check valve, the back-check valves being arranged in such amanner that their flow directions are unidirectional.
 2. Thedouble-acting refrigerant compressor according to claim 1, wherein thepiston and the cylinder portions are formed with rotational symmetry,the back-check valves and the flow channel being arranged on the centrallongitudinal axis of the piston and the cylinder portions.
 3. Thedouble-acting refrigerant compressor according to claim 1, wherein thecylinder portions are spaced from each other in such a manner that aregion of the piston is freely accessible from outside the cylinderportions.
 4. The double-acting refrigerant compressor according to claim1, wherein, between the piston and each cylinder portion, a respectivecompressible working volume is formed adjacent to the back-check valveof the respective cylinder portion and to the back-check valve of thepiston.
 5. The double-acting refrigerant compressor according to claim1, wherein the piston on an end side thereof comprises a low-pressurecompression face and on the opposite side comprises a high-pressurecompression face which is smaller than the low-pressure compressionface.
 6. The double-acting refrigerant compressor according to claim 5,wherein the valve of the piston is formed in the high-pressurecompression face.
 7. The double-acting refrigerant compressor accordingto claim 5, wherein the piston comprises, between the low-pressurecompression face and the high-pressure compression face, an auxiliarycompression surface which, together with the cylinder portion formingthe low-pressure working volume, forms an auxiliary volume.
 8. Thedouble-acting refrigerant compressor according to claim 1, wherein atleast one cylinder portion is guided as an inverse piston in the piston.9. The double-acting refrigerant compressor according to claim 1,wherein the piston is driven in a contactless manner by two solenoidsoperating in opposite senses.
 10. The double-acting refrigerantcompressor according to claim 1, wherein the piston is guided by a crankdrive via an eccentric guide arrangement.
 11. The double-actingrefrigerant compressor according to claim 1, wherein the piston isprovided with an “8”-shaped sliding track engaged by a nose of a rotarydrive for driving the piston.